Daily Variations in the Production of Aflatoxins by Aspergillus flavus NRRL‐3145 Following Exposure to 60 Co Irradiation

S ummary . Spores of the toxigenic fungus Aspergillus flavus NRRL‐3145 were exposed to γ‐irradiation and allowed to germinate. The increase in the production of aflatoxins B 1 and B 2 following inoculation on cracked red wheat or in a liquid synthetic medium was greater than that which occurred in similarly treated cultures derived from non‐irradiated spores. Variations in aflatoxin production were also observed daily for both the control and irradiated cultures developing on both media, with maximum toxin production varying from 2–10 days of incubation. The most notable increases in aflatoxin production occurred from cultures that developed from spores irradiated with 150, 200 or 300 krad. Exposure to 400 or 600 krad resulted in the complete inhibition of spore germination and, consequently, no aflatoxin was produced. The quantities of B 2 toxin produced were significantly lower than that of B 1 toxin, except in the synthetic medium where B 2 production was comparable with that of B 1 . Cultures developing from non‐irradiated spores exhibited a diphasic curve in production of aflatoxin G 1 when grown on wheat, with maximum toxin production occurring on the 4th and 10th day of incubation, while in the synthetic medium, G 1 production occurred as a monophasic curve. In the wheat, irradiation of A. flavus spores with 25, 100, 150, 200 or 300 krad caused significant increases of G 1 toxin over the amounts of the same toxin produced by non‐irradiated controls. Similarly, exposure of spores to 200 krad and subsequent growth in a liquid synthetic medium resulted in significant increases in the amounts of G 1 toxin produced compared with non‐irradiated controls. Except for the 200 krad irradiation, the amounts of G 2 toxin produced daily by spores were generally lower than those of G 1 toxin in either the wheat or the synthetic medium. Media, time of incubation and selected irradiation levels affected the daily and total amounts of aflatoxins produced.